F. B. Loomis — Turtles from the Upper Harrison Beds. 19 



Fig. 



(32 mm ). The jugal arch is unusually heavy, being 19 mm wide 

 at the narrowest part. The palate is high vaulted and rather 

 narrow. The masticatory surfaces of the maxillae are wide, 

 aud have three ridges, and two longitudinal grooves. The mar- 

 ginal ridge is high and sharp, slightly dentate and overlaps the 

 mandible extensively. The median ridge is low but acute, 

 while the innermost one is rounded and crossed by shallow 

 striae. The two inner ridges do not continue onto the pre- 

 maxillae, which have a deep depression, into which evidently 

 fitted a strong horny tooth on the lower jaw. The posterior 

 nares open far enough back so that they are behind the shelf 



just described. On either ptery- 

 goid there is a slightly hooked 

 ecto pterygoid process. 



The lower jaws are rather nar- 

 row, 26 mrn high at the coronoid, 

 and the upper margin contains 

 a deep groove, bounded by two 

 sharp edges, of which the inner 

 is the higher. 



Of the carapace but a small 

 portion of the rear was pre- 

 served, but that fortunately 

 included the half of the pygal, 

 suprapygal and the eleventh 

 peripheral, which correspond 

 almost exactly in dimensions and 

 thickness with those of the type, 

 so that the association may be 

 considered unquestionable, inas- 

 much as the two came from 

 within a mile or two of each 

 other. 



Of the plastron the anterior 

 lobe of the left side and some 

 fragments were found. The 

 whole lobe is about 330 mm wide 

 and 240 mm long, indicating that 

 the shell was relatively long 

 and narrow. The lip is prominent, being 148 mm wide at the 

 base and T5 mm long on the median line. The anterior corners 

 are rounded and there is a small notch in front, making a form 

 in itself distinctive. From the front, the lip thickens rapidly 

 until, when 115 mm back, it is T5 mm thick. It then drops down 

 abruptly, the escarpment being strongly excavated behind. 

 The following measurements of plastral scutes are all that can 

 be given : On the median line, the gulars occupy 125 mm , 

 humerals 105 mm , and the pectorals but 15 mm . 



Fig. 2. The anterior portion of 

 the plastron of T. arenivaga. % 

 nat. size. 



